The Dupont isolator system is a lysis-centrifugation blood culture system which has been found by some investigators to yield more rapid results as well as to have greater sensitivity for detection of yeast and staphylococci in blood. There has been some variability in the results reported by different investigators, but the major findings so far suggest that lysis-centrifugation may be superior to routine methods for at least certain organisms. Three patient-care services of the Clinical Center (2 oncology and 1 intensive care) cooperated in an evaluation of the Isolator technique for blood cultures drawn on their patients. Blood specimens for culture were simultaneously drawn into one routine blood culture bottle and one isolator tube. Information as to the type of organisms isolated, time to detection of a positive culture, and time to obtain growth for susceptibility testing and identification was compiled and analyzed. In addition to comparing the Isolator to a routine blood culture bottle, a simultaneous comparison to a lysis-filtration system was also performed on the same blood cultures.